This is the 15th year of this training grant for post-doctoral research training focused on M.D., Ph.D., and M.D./Ph.D. scientists. The training centers on the Department of Pathology and Immunology at Washington University. We have a faculty of seventeen distributed among five departments, but having a high representation in Pathology and Immunology. The faculty is made up of a highly collegial group of immunologists and cell/molecular biologists who have interacted heavily for several years. The research of much of the faculty is on various aspects of immunology and host resistance, but also includes a heavy emphasis on the molecular basis of cell activation (for example among several, are projects on the host response to tumors and to herpes viruses, lymphocyte differentiation and activation, cell biology and biochemistry of antigen processing, the molecular basis and analysis of cell interaction molecules, regulation of DNA cycle). There are two sets of trainees. Trainees are either M.D.'s or M.D./Ph.D.'s who want to have a serious and in-depth experience in research following their clinical training in Pathology. Or fellows with a graduate degree or an M.D., not associated with Pathology clinical training, having an interest in the research done by any of the faculty members: we have an applicant pool of about 100 (non-foreign), with a total of 68 postdoctoral fellows among the seventeen laboratories. Of these, nine are supported by this training grant. We now solicit ten training positions. A Steering Committee of five senior faculty members oversees the training and is responsible for the selection of trainees. Training includes a 2-3 year period of full-time research experience in the laboratory, where the trainee is exposed to the latest approaches in cell and molecular biology (transgenic and knockout facilities, peptide chemistry, DNA technology). Part of the training includes laboratory meetings and reports, attendance to weekly seminars, and opportunities for courses in Cancer Biology. Of 44 trainees that have graduated from this Program, 88 percent continue in research, with 65 percent in faculty positions, mostly in Pathology.